Mets closer Bobby Parnell will need neck surgery to repair a herniated disk, according to Mets manager Terry Collins, who had said Sunday Parnell had planned to wait until mid-September to make the decision.

Last month, Parnell had said if he had to undergo surgery, he expected to be ready for spring training. Monday, Collins tentatively agreed with that timeline.

Parnell, who had 22 saves with a 2.16 ERA this season, has been on the disabled list since Aug. 6.

The Mets added veteran right-handed pitcher Aaron Harang, outfielder Mike Baxter and catcher Juan Centeno to the major league roster Monday, and they’re expected to add the 35-year-old Harang to their starting rotation on Thursday against the Nationals.

“They told me I’d slide in there and pitch on Thursday,” Harang said. “I came in, got a bullpen [session] in today. It fits me right into [the rotation] schedule-wise when I was throwing down in Las Vegas.

“The biggest thing was to be in the rotation and hopefully be the veteran that can help answer questions for the younger guys, and just finish out my season on a strong note was the biggest thing. Here it was getting a chance to finish out the season in the rotation.”

The Mets will push Jon Niese back a day, having him start Friday against the Marlins.

“Zack [Wheeler], even though he didn’t throw a lot of pitches, said he wanted to come back on regular rest, he feels comfortable doing that,’’ Collins said. “Jon said, ‘I don’t care what you do.’ So we’ll have Jon pitch Friday night to open the Miami series. Nobody’s hurt, everybody’s fine.’’

If he gets in a game, Centeno would be making his major league debut.

The Mets reportedly are set to play two exhibition games against the Blue Jays at Montreal’s Olympic Stadium near the end of next spring training, an agreement first reported by Sportsnet.ca. The Mets haven’t played there since Sept. 23, 2004.